1. Field of the Invention
The present invention relates to an electrical connector device which provides electrical connection between relatively rotatable components, i.e. between components located on a rotatable side and a stationary side.
2. Description of the Prior Art
It has been known to use a slip-ring assembly for providing electrical connection between electrical devices arranged on a side of a rotary shaft and a stationary side, respectively. Specifically, a brush is fixedly provided on the stationary side and arranged to slide on a slip-ring which is fixedly provided along circumference of the rotary shaft, so as to maintain the electrical connection therebetween.
However, in this prior art, since the electrical connection is maintained by the mechanical sliding relationship between the slip-ring and the brush, short circuits due to metal powder caused by the sliding action therebetween as well as imperfect or defective contacts therebetween due to invasion of dust are likely to occur, which can not be effectively avoided. Accordingly, a problem has been raised on reliability particularly when it is used, such as, in a triggering circuit for an airbag provided in an automotive steering wheel, where a reliable transmission of a triggering current is extremely required.
In order to solve this problem, there has been proposed another type of the electrical connector device as disclosed in, such as, Japanese First (unexamined) Patent Publication No. 57-165982 which is equivalent to U.S. Pat. No. 4,502,746. In the electrical connector device of this type, an electrically conductive member is loosely wound around a rotary shaft with its one end fixed to the rotary shaft and with its other end fixed to a stationary side so as to ensure the electrical connection therebetween.
FIG. 9 shows an electrical connector device similar to the latter prior art, for briefly explaining the concepts incorporated in the latter prior art. In FIG. 9, FIG. 9(A) shows a transverse cross section of the electrical connector device and FIG. 9(B) shows a vertical cross section thereof.
A stationary member 72 of an annular-cylindrical shape is provided surrounding a rotary shaft 71 to define an annular space therebetween. A flexible cable 73 is arranged in the annular space as being loosely wound around the rotary shaft 71. One end of the cable 73 is fixed to the rotary shaft 71 and electrically connected to a first terminal 74 for connection to an electric device arranged at a location for co-rotation with the rotary shaft 71. The other end of the cable 73 is fixed to the stationary member 72 and electrically connected to a second terminal 75 for connection to an electric device arranged on the side of the stationary member 72.
With this arrangement, when the rotary shaft 71 rotates in a counter-clockwise direction, the rotary shaft 71 pulls the cable 73 so that the cable winding is contracted onto the rotary shaft 71, while, when the rotary shaft 71 rotates in a clockwise direction, the rotary shaft 71 pushes the cable 73 so that the cable winding expands to be loosened. In this manner, the rotary shaft 71 is allowed to rotate within a limited number of revolutions or turns.
In this latter prior art, however, since an overall length of the cable 73 is determined depending on a diameter of the rotary shaft 71 and a required limited or maximum number of revolutions of the rotary shaft 71, when the diameter of the rotary shaft 71 increases, the length of the cable 73 as well as the size of the stationary member 72 which accommodates the cable 73 therein, inevitably increase, respectively.